[OSM-dev] Extracting national boundaries

Andy Deakin andy.deakin at pcmend.net
Mon Aug 30 10:12:12 BST 2010


Hi Colin,

I went through exactly the same process some time ago, and eventually 
used a different source:
http://thematicmapping.org/downloads/world_borders.php

It would be nice to be able to extract something very similar from osm. 
If you have any success, please share it.

Andy

On 30/08/10 10:05, Colin Smale wrote:
>  Hi,
>
> I am trying to extract national boundaries from OSM and it's proving 
> more difficult than I anticipated.
>
> What I would like to end up with, is a collection of complex polygons 
> (inner and outer rings including enclaves/exclaves), one for each 
> country. I thought I should be able to do that by getting all 
> relations with type=boundary, admin_level=2. Using XAPI I got a large 
> file which contains some of the information, but as some national 
> boundaries seem to be implemented using subrelations and 
> subsubrelations etc I now find I will have to query the database for 
> each subrelation individually and drill down successively until I have 
> all the ways I need. But that looks as if it will give me large 
> numbers of internal borders between lower-level admin units as well, 
> and it will be an enormous job to stitch everything together and 
> discard the internal borders.
>
> For many countries there is a simple relation for the national 
> boundary, referencing a number of ways, which I can concatenate to 
> produce the complete outer boundary. But France and Slovakia for 
> example don't seem to have a single relation as a starting point.
>
> I can't imagine I am the first person to want to do this. Has anyone 
> got any tips? Or maybe even a ready-made data set?
>
> National boundaries don't change all that often, but it does happen 
> from time to time, so it would be nice if this could be repeatable in 
> the future.
>
> Thanks in advance for any help you can give!
>
> Regards,
> Colin
>
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